JPH0259660A - Crack detecting method - Google Patents

Abstract

PURPOSE:To improve the discrimination accuracy for the generation of a crack by discriminating whether a point shown by a natural frequency and an output level of a wave type of its natural frequency is within a prescribed area of a two-dimensional plane consisting of the frequency and the output level or not. CONSTITUTION:A percussion is given to an article to be inspected 1 by a steel ball 3, and its vibration is detected by an electromagnetic pick 5, amplified by an amplifier 7 and outputted to a frequency analyzer 9. The frequency analyzer 9 inputs a vibration waveform, based on a timing signal outputted from a delay device, and analyzes a frequency component of a frequency waveform and its output level. Subsequently, whether a point shown by a natural frequency of the frequency waveform and its output level is in a prescribed closed area which is set at every natural oscillation by a setting device 11, of a two-dimensional plane in which the frequency and the output level are parameters or not is discriminated by a discriminator 10. In such a way, the discrimination accuracy for the generation of a crack can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for non-destructive testing of inspected items, which are sintered parts, and particularly relates to a method for non-destructive testing of inspected items, which are sintered parts. The present invention relates to a crack detection method using a impact vibration analysis method, which determines the quality of the inspected product through analysis.

[Conventional technology]

Conventionally, one of the nondestructive testing methods for determining the quality of metal members is the so-called impact vibration analysis method, which detects cracks in the inspected member by applying a blow to the metal member and detecting the vibration sound.

As a conventional example of this impact vibration analysis method, for example,
As disclosed in Japanese Patent No. 8-30983, there is a method of determining cracks based on the natural frequency of natural vibration caused by impact.

In addition, for example, as disclosed in "Evaluation of Mechanical Properties and Cracks of Metal Materials by Impact Vibration Analysis Method"; Material No. 3844 of the Third Subcommittee of the Japan Nondestructive Inspection Association, it is possible to use the natural frequency and damping coefficient of impact vibration. There are also methods to predict the occurrence of cracks.

This impact vibration analysis method processes the detection signal from the sensor that detects the vibration generated by impact, obtains the auto power spectrum and the envelope of the waveform, calculates the natural frequency and amplitude damping coefficient, and The occurrence of cracks is determined based on the magnitude of the natural frequency and amplitude damping coefficient.

[Problem to be solved by the invention]

As disclosed in Material No. 3844 of the Third Subcommittee of the Japan Nondestructive Testing Association, generally, the damping coefficient increases when a crack occurs, and the natural frequency decreases when a crack occurs.

However, some defective products with cracks have damping coefficients that are smaller than those of good products without cracks, and there are also products with natural frequencies that are equal to those of good products without cracks. However, there was a problem in that the discrimination accuracy was not sufficient based only on the magnitude of the natural frequency or the damping coefficient.

Therefore, it is an object of the present invention to improve the accuracy of determining the occurrence of cracks by combining and determining both the natural frequency and the output level of the waveform of the natural frequency.

[Means to solve the problem]

Therefore, in the present invention, a closed area of a non-defective product is set in advance on a two-dimensional plane using the output level of the waveform of the natural frequency and its resonance frequency as parameters, and the natural frequency of the product to be inspected and its natural The present invention is characterized in that crack detection is performed based on whether the output level of the vibration waveform is located within the closed area.

Specifically, the sound or vibration generated by hitting the inspected item is detected, the detection signal is sampled at a predetermined sampling time from the predetermined point of impact, and the natural vibration is determined from this sampled detection signal. Find the natural frequency and the output level of the natural vibration, and find the point on the two-dimensional plane expressed by the natural frequency and the output level of the natural vibration on the two-dimensional plane with the frequency and the output level as parameters. The present invention is characterized in that the quality of the inspected product is determined by determining whether or not it is within a predetermined closed area.

[Effect]

According to the configuration of the present invention, whether a point expressed by the frequency of the vibration and the output level of its natural frequency is within a predetermined closed area on a two-dimensional plane with both the frequency and the output level as parameters. Since it is possible to determine whether a product is good or not based on whether the product is good or not, it is possible to accurately determine whether the product is good or bad even if the product under inspection would be misjudged based on the output level of the natural frequency or its natural frequency component alone. Can be distinguished.

〔Example〕

Next, a crack detection method according to an embodiment of the present invention will be explained in detail with reference to FIGS. 1 to 4.

1 to 4 are diagrams for explaining a crack detection method according to an embodiment of the present invention. FIG. 1 is a block diagram of an inspection device used in the crack detection method, and FIG. 2 is a block diagram of a crack detection method. FIG. 3 is a waveform diagram showing the vibration waveform of impact vibration of the inspected product, and FIG. 4 is a frequency spectrum diagram of the vibration waveform.

In FIG. 1, reference numeral 1 denotes an item to be inspected, and reference numeral 2 denotes an inspection jig, and the item 1 to be inspected is supported by this inspection jig 2. In FIG. Reference numeral 3 designates a steel ball for striking the inspected item 1, which is suspended from a predetermined height with a predetermined length of piano wire. Reference numeral 4 is a microphone, reference numeral 5 is an electromagnetic pick that detects vibrations based on changes in the distance to the inspected product 1, and reference numeral 6 is an acceleration pick that is fixed to the vibrating part and directly detects vibrations, which detects the sound when struck by the steel ball 3. is detected by a microphone 4, and impact vibration is detected by an electromagnetic pick 5 or an acceleration pick 6. microphone 4
, the electromagnetic pick 5, or the acceleration pick 6, the only difference is the method of detecting impact vibration, and the subsequent discrimination method is the same, so the same result can be obtained no matter which method is used for detection.

In the figure, the microphone 4, electromagnetic microphone 5, and acceleration pink 6 are arranged in parallel for convenience, but in reality,
Either one is used.

Hereinafter, a case where the electromagnetic pick 5 is used will be explained.

Reference numeral 7 is an amplifier that amplifies the output signal from the electromagnetic pick 5.

Reference numeral 8 denotes a delay device that outputs a timing signal based on the vibration waveform from the amplifier 7, which instructs the timing to take in the vibration waveform from the time of impact.

Here, the timing signal will be explained with reference to FIG. 3. FIG. 3 shows the vibration waveform from the amplifier 7. Waveform A represents the impact noise at the time of impact, and the impact noise A includes a wide range of frequency components similar to white noise.
The amplitude also fluctuates significantly. Waveform B is the impact noise A
The vibration waveform of the inspected product 1 after being attenuated shows a resonance phenomenon due to the natural frequency, so it forms a curve like waveform C shown by a dotted line.

Since the impact noise A is a vibration unrelated to the natural vibration of the product 1 to be inspected, if this waveform is taken in and subjected to frequency analysis, an erroneous determination will occur. Therefore, in order to eliminate the influence of this impact noise A, 1. A timing signal that instructs sampling for a time t5 is generated with a delay of 50 minutes, and after tt has elapsed from the moment of impact, a timing signal that instructs a second sampling for a time t3 is generated again.

Note that in order to remove the influence of resonance, the sampling time t3 is larger than the period of the waveform C waveform, and (t!-
t, )/2.

In this way, sampling timing 1. ．． By setting 1° and sampling time t, stable and highly accurate determination can be made.

Reference numeral 9 denotes a frequency analyzer that analyzes and outputs the frequency component of the vibration waveform detected by the electromagnetic pick 5 and its output level.

The frequency analyzer 9 is capable of detecting the output level of each frequency, as shown in the frequency spectrum diagram of FIG. 4 showing the frequency components of the vibration waveform and their output levels. In the present embodiment, the peak value P1 representing the natural frequency and output level of the first to third natural vibrations shown in FIG. P2. P3 can be detected. High-order natural vibrations of the fourth order or higher have small peak values and lower detection sensitivity, so they are not used in this embodiment.

Reference numeral 10 indicates the natural frequencies of the first to third order natural vibrations of the vibration waveform output from the frequency analyzer 9 and their output levels PI, P2 . It is determined for each of the first to third natural vibrations whether or not P3 exists within a predetermined closed area on a two-dimensional plane with the frequency and output level as parameters, and
This is a discriminator that determines that a product is good only when the following natural frequencies and their output levels are all within the closed range.

Reference numeral 11 is a setting device for setting the predetermined closed region for each of the first to third natural vibrations.

As shown in FIG. 3, the predetermined closed area indicating a non-defective product, which is set by the setting device 11, is determined by selecting a plurality of non-defective products and defective products in advance, and selecting the first to third natural frequencies and outputs. Detect levels. Then, plot this natural frequency and output level on a two-dimensional plane with the frequency and output level as parameters, that is, a two-dimensional plane with the frequency as the x-axis and the output level as the y-axis, and from the distribution. , find the center of gravity position, and calculate the long axis of the ellipse (X
(axis) and short axis (y-axis), find the standard deviation (=sigma) in each direction, set 3 sigma as the major axis (α) and minor axis (β) of the ellipse, and calculate the area surrounded by this ellipse. The closed area is determined to be a good product, and this is set as 1 to 3.
Set each of the following natural vibrations.

In the figure, ○ indicates the natural frequency and its output level of a good product, and × indicates the natural frequency and its output level of a defective product. This figure shows the distribution of secondary natural vibrations. Then, ■.Set the third-order natural vibration in the same way.

Next, the operation of this embodiment will be explained.

First, the item to be inspected 1 is set on the inspection jig 2, and the steel ball 3 is dropped naturally from a predetermined height and collides with the vertical surface of the item to be inspected 1 at right angles to give a blow.

The vibration caused by this impact is detected by the electromagnetic pick 5, and the vibration waveform from the electromagnetic pick 5 is amplified by the amplifier 7 and output to the frequency analyzer 9 and the delay device 8. The delay device 8 detects the point of impact from the vibration waveform, and outputs a timing pulse instructing frequency analysis to the frequency analyzer 9 at a predetermined timing from this point of impact. Based on the timing pulse from the delay device 8, the frequency analyzer 9 analyzes the frequency of the vibration waveform from the amplifier 7, and calculates the first to third natural frequencies of the vibration waveform and the output level at the natural frequencies. In search of
A signal indicating the natural frequency and its output level is output to the discriminator 10. In this discriminator 10, a signal indicating the natural frequency and its output level from the frequency analyzer 9 is used as a parameter for a non-defective product on a two-dimensional plane with the frequency and output level preset in the setting device 11 as parameters. If the natural frequencies and output levels of the first to third order natural vibrations are all within the closed range, a pass signal indicating that the product is good is determined. Further, if any one of the first to third conditions is outside the closed range, a rejection signal indicating that the product is defective is output.

According to this embodiment, since pass/fail is determined based on the three components of the first to third orders of the natural vibration of the vibration waveform, cracks can be detected more accurately.

Further, since the frequency analysis is performed after a predetermined period of time has elapsed from the start of impact, taking into consideration the propagation time of impact vibration, it is possible to prevent misjudgment due to impact noise during impact, and to accurately detect cracks.

〔Effect of the invention〕

As described above, according to the present invention, a point represented by a natural frequency and an output level of the natural frequency is within a predetermined closed area on a two-dimensional plane in which both the frequency and the output level are parameters. Since it is determined whether the product is good or not based on whether or not it exists, even if the product under inspection would be misjudged based on the magnitude of the natural frequency or the output level of its natural frequency component, it can be accurately detected. It has the excellent effect of being able to determine whether it is good or bad.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining a crack detection method according to an embodiment of the present invention. FIG. 1 is a block diagram of an inspection device used in the crack detection method, and FIG. 2 is a block diagram of a crack detection method. FIG. 3 is a waveform diagram showing the vibration waveform of impact vibration of the inspected product, and FIG. 4 is a frequency spectrum diagram of the vibration waveform. 1...Product to be inspected

Claims (1)

[Claims] (1) Detect the sound or vibration generated by hitting the item to be inspected, sample the detection signal at a predetermined sampling time from the point of impact, and extract the characteristic from this sampled detection signal. The natural frequency of vibration and the output level of the natural vibration are determined, and the point represented by the natural frequency and the output level of the natural vibration on a two-dimensional plane with the frequency and the output level as parameters is located on the two-dimensional plane. A crack detection method characterized in that the quality of a product to be inspected is determined by determining whether or not the product is within a predetermined closed area.